AM/FM receiver using spectral parameter estimators

ABSTRACT

An AM/FM receiver which demodulates radio signals by computing estimates of spectral parameters of the radio signals. Three spectral parameter estimation circuits are selectively formed from a number of shared circuits according to the type of modulation of the radio signal. In the case of frequency modulated signals, the respective strengths of the desired signal and interfering signals dictate the most favorable circuit configuration. The first estimation circuit calculates the instantaneous amplitude of the radio signal which corresponds to the modulating audio signal of an AM signal, the second estimation circuit calculates the instantaneous frequency of the radio signal which corresponds to the modulating audio signal of an FM signal, and the third estimation circuit calculates the power mean frequency of the radio signal which, when calculated over a short period of time relative to the rate of change of the FM signal, also corresponds to the modulating audio signal.

BACKGROUND OF THE INVENTION

This invention relates to AM/FM radio receivers and to demodulatingcircuits for such receivers.

In a radio receiver, a detector or demodulator circuit is necessary inorder to provide at its output a signal which varies according to themodulation of the radio signal. This signal may then be amplified byaudio amplification circuits and used to drive some acoustic signalgenerating means in order to make the audio component capable of beingheard by the human ear.

It is desirable to implement radio receivers using integrated circuittechnology; however, most prior detectors utilize inductors which cannotbe implemented using integrated circuits.

SUMMARY OF THE INVENTION

In accordance with this invention, an AM/FM receiver accomplishesdemodulation of AM and FM signals through spectral parameter estimationcircuits which are selectively formed from shared apparatus inaccordance with the type of signal modulation and other characteristicsof the received signal.

The circuit of this invention requires no inductors and may, therefore,be advantageously implemented using integrated circuit technology. Thisinvention may also be used to perform the mixer and IF amplifierfunctions by connecting the output of an RF amplifier directly to theinput of the invention. An integrated circuit utilizing this inventionmay, therefore, replace a large portion of a conventional receiver.

BRIEF DESCRIPTION OF THE DRAWING

A radio receiver circuit according to this invention will be betterunderstood from a consideration of the detailed description of theorganization and operation of one illustrative embodiment thereof whichfollows when taken in conjunction with the accompanying drawings inwhich:

FIG. 1 depicts a block diagram of a radio receiver according to thisinvention;

FIG. 2 depicts a more detailed block diagram of a receiver circuitaccording to this invention and having the signals present at each stagelabeled thereon; FIGS. FIG. 3 and 4 depict alternative signaltranslating circuits for use in the circuit of FIG. 2; and

FIG. 5 - 7 depict a schematic diagram of a detector according to thisinvention.

DETAILED DESCRIPTION

One illustrative AM/FM receiver according to this invention is shown inFIG. 1 for generating an acoustic signal corresponding to the audiocomponent of a radio frequency signal received on an antenna 10. Theoutput of antenna 10 is connected to an RF amplifier 11 which amplifiesthe received RF signal in order to drive the remaining circuitry. Theoutput of RF amplifier 11 is connected to an input of a first mixercircuit 51. A reference signal generator 13 generates a reference signalat a frequency ω_(o) and has two outputs, one for presenting an outputsignal corresponding to Sine ω_(o) t and one for presenting an outputsignal corresponding to Cosine ω_(o) t. The reference frequency ω_(o)corresponds to the center frequency of the input signal to bedemodulated and ω_(o) may be fixed or tunable according to theparticular application of the receiver. The output signal of referencesignal generator circuit 13 corresponding to Sine ω_(o) t is connectedto an input of mixer circuit 51. The output of mixer circuit 51 isconnected to the input of a low pass filter 52. The signal present onthe output of low pass filter 52 corresponds to only certain lowfrequency components of the signal present on the input of low passfilter 52. The output of low pass filter 52 is a signal corresponding tothe Sine of the difference between input signal frequency ω_(i) and thereference signal frequency ω_(o). The output of low pass filter 52 isconnected to the input of an audible tuning indicator switch 14 and theoutput of switch 14 is connected to the input of a differentiatorcircuit 15. When switch 14 is in the first position, such that a closedpath is present between the output of low pass filter 52 and the inputof differentiator circuit 15, no tuning indication is present. Whenswitch 14 is in the second position, such that there is no connectionbetween the output of low pass filter 52 and the input of differentiatorcircuit 15, an audible tuning indicator is present in the acousticoutput signal in the form of a tone whose frequency corresponds to thedifference frequency ω_(i) - ω_(o). The audible tuning indicator tonedecreases in frequency as the input signal is correctly tuned in.Differentiator circuit 15 generates at its output a signal correspondingto the mathematical derivative of its input signal. Since analogdifferentiator circuits are inherently inaccurate in that they do notgenerate the same phase shift between input and output over a range offrequencies, the output of low pass filter 52 is also connected to theinput of a phase compensator circuit 16 which generates an output signalcorresponding to the input signal phase shifted by an amount such thatthe outputs of differentiator circuit 15 and phase compensator circuit16 maintain a constant 90° phase relationship over a range offrequencies. A digital circuit implementation of the invention would notrequire a phase compensation circuit since a digital differentiatorcircuit is inherently more accurate than an analog differentiatorcircuit.

The output of RF amplifier 11 is also connected to a input of a secondmixer circuit 55. The output of reference signal generator circuit 13 isconnected to another input of mixer circuit 55. The output of mixercircuit 55 is connected to the input of a low pass filter 56. The signalpresent on the output of low pass filter 56 corresponds to only certainlow frequency components of the signal present on the input of low passfilter 56. The output of low pass filter 56 which corresponds to theCosine of the difference between the input signal frequency ω₁ and thereference signal frequency ω_(o) is connected to the input of adifferentiator circuit 18 which generates an output signal correspondingto the mathematical derivative of its differentiator input signal. Theoutput of low pass filter 56 is also connected to an input of a phasecompensator circuit 19 which generates an output signal corresponding toits input signal phase shifted by an amount such that the phaserelationship between the outputs of phase compensator 19 anddifferentiator 18 remains a constant 90° over a range of frequencies.

A power frequency product circuit 20 comprises four inputs connected,respectively, to the outputs of differentiator 15, phase compensator 19,phase compensator 16, and differentiator 18, and means for generating anoutput signal corresponding to the product of the input signal powertimes the instantaneous absolute difference in frequency between theinput signal frequency and the reference signal frequency.

A power circuit 21 comprises two inputs connected, respectively, to theoutputs of phase compensator circuit 19 and phase compensastor circuit16, and means for generating an output signal corresponding to the powerof the input signal.

A mode selection switch 30 comprises five single-pole three-positionswitches which are physically coupled together. Mode switch 30 has threepositions corresponding, respectively, to FM detection by means of apower frequency estimator, FM detection by means of an instantaneousfrequency estimator, and AM detection by means of an instantaneous powerestimator.

When mode switch 30 is in its first position, the output of powerfrequency product circuit 20 is connected through switch 34 to the inputof an integrator circuit 40 which provides a signal at its outputcorresponding to the time average of its input signal over apredetermined period of time. The output of power circuit 21 isconnected through switch 35 to the input of integrator circuit 41. Theoutput of integrator circuit 40 is connected through switch 31 to thedivident input of a divider circuit 42. The output of integrator circuit41 is connected through switch 32 to the divisor input of the dividercircuit 42. The output of divider circuit 42, corresponding to aquantity which represents the quantity present on the dividend inputdivided by the quantity present on the divisor input, is connected tothe input of a de-emphasis circuit 46. The output of de-emphasis circuit46 corresponds to the signal present on the input of circuit 46 with thehigh frequency components attenuated by a certain factor to compensatefor the emphasis provided by the transmitter. The output of de-emphasiscircuit 46 is connected to the input of an audio amplifier 43 throughswitch 33 which generates an output signal corresponding to the inputsignal amplified such that it can drive an acoustic signal generatingdevice 44 which has its input connected to the output of the audioamplifier 43.

When mode switch 30 is in its second position the output of powerfrequency product circuit 20 is connected through switch 31 to thedividend input of divider circuit 42. The output of power circuit 21 isconnected through switch 32 to the divisor input of divider circuit 42.The output of divider circuit 42 is connected through switch 34 to theinput of integrator circuit 40. The output of integrator circuit 40 isconnected through de-emphasis circuit 47 and switch 33 to the input ofaudio amplifier 43.

When mode switch 30 is in its third position, corresponding to AMdetection, the output of power circuit 21 is connected to the input of asquare root circuit 45 which generates an output signal corresponding tothe mathematical square root of its input signal. The output of squareroot circuit 45 is connected through switch 35 to the input ofintegrator 41. The output of integrator 41 is connected through switch33 to the input of audio amplifier 43.

The circuit shown in FIG. 1 may be adapted to receive stereo FM signalsby techniques well known in the art, namely deleting circuits 46 and 47and replacing circuits 43 and 44 with a stereo demodulator comprising aninput connected to the output of switch 33 and an output for each of thetwo stereo channels. Each output of the stereo demodulator would beconnected to a de-emphasis circuit followed by an audio amplifier and anacoustic signal generating device.

An AM/FM receiver such as illustrated in FIG. 1 may be implemented usingeither digital or analog techniques. An exemplary analog circuitimplementation is shown in more detail in FIG. 2; however, the principleof the invention extends both to digital and analog implementations. Adigital implementation of each of the elements of the circuitimplementation described herein is fully disclosed in my applicationknown as Denenberg 2, Ser. No. 545,410 filed on Jan. 30, 1975.

One illustrative AM/FM receiver circuit according to this invention isshown in FIG. 2 as a circuit for generating an acoustic signalcorresponding to the audio component of a radio frequency signalreceived on the antenna 10. An input signal received on antenna 10 isrepresented as a sinusoidal signal of the form x Cos ω_(i) t where x isthe amplitude of the input signal, ω_(i) is the instantaneous frequencyof the input signal in radians per second, i.e., ω= 2πf where f is thefrequency in hertz and t represents the time varying nature of the inputsignal. The output of antenna 10 is connected to an RF amplifier 11which amplifies the received RF signal in order to drive the remainingcircuits.

The output of RF amplifier 11 is connected to the input of a splitternetwork 50 which presents two output signals of the same form as thesignal applied to its input. The reference signal generator 13 comprisesan oscillator which has two outputs for presenting signals correspondingrespectively to Sin ω_(o) t and Cos ω_(o) t where ω_(o) is a referencefrequency which is the center frequency at which the receiver receivesinput signals.

An output of splitter circuit 50 and the output of reference signalgenerator 13, corresponding to Sin ω_(o) t, are connected to respectiveinputs of mixer circuit 51. An exemplary mixer circuit such as iscontemplated for use in this invention comprises an analog multipliercircuit having two inputs, an output, and means for generating at theoutput a signal corresponding to the mathematical product of the twonumbers represented by the signals present at the inputs. The product ofthe two signals applied to mixer 51, x Cos ω_(i) t and Sin ω_(o) t, is asignal having components representing both the sum and difference of thetwo frequencies as follows:

    x Sin (ω.sub.i - ω.sub.o)t + x Sin (ω.sub.i + ω.sub.o)t                                           (1)

The output of mixer 51 is connected to the input of a low pass filter 52whose bandpass characteristic is arranged such that the signal componentcorresponding to the sum of ω_(i) and ω_(o) is removed, leaving

    x Sin (ω.sub.i - ω.sub.o)t                     (2)

A low pass filter comprises an input for receiving an input signal andan output for providing a signal corresponding to only those componentsof the input signal having a frequency less than a certain cutofffrequency. Low pass filter 52, in addition to removing the signalcorresponding to the sum of the two frequencies ω_(i) and ω_(o), is alsodesigned to perform the function of an Intermediate Frequency (IF)amplifier, namely to filter out all signals outside the range offrequencies corresponding to the bandwidth of the desired signal andthereby removing signals adjacent to the desired signal. The output oflow pass filter 52 is connected to the input of a differentiator circuit15 which generates a signal at its output corresponding to the firstderivative of the input signal (2) which is

    x (ω.sub.i - ω.sub.o) Cos (ω.sub.i - ω.sub.o)t (3)

A differentiator circuit may be constructed from a low pass filtercircuit having certain predefined characteristics. The output of lowpass filter 52 is also connected to an input of phase compensationcircuit 16. A phase compensation circuit such as is contemplated for usein this invention comprises, for example, a low pass filter havingpredefined characteristics such that its output is phase shifted wherebythe phase difference between the outputs of differentiator 15 and phasecompensation circuit 16 are constant over a range of frequencies.

The output of reference signal generator 13, corresponding to Cos ω_(o)t, is connected to a first input of a mixer circuit 55, and an output ofsplitter circuit 50 is connected to a second input of mixer circuit 55.The output of mixer circuit 55 is the product of the two input signals,x Cos ω_(i) t and Cos ω_(o) t, which is:

x Cos (ω_(i) - ω_(o))t + x Cos (ω_(i) + ω_(o))t (4)

The output of mixer 55 is connected to the input of a low pass filter 56whose bandpass characteristic is arranged such that the signal componentcorresponding to the sum of ω_(i) and ω_(o) in (4) is removed, leaving

    x Cos (ω.sub.i - ω.sub.o)t                     (5)

The output of low pass filter 56 is connected to the input of adifferentiator circuit 18 which generates at its output a signalcorresponding to the first derivative of the input signal (5), which is

    x (ω.sub.i - ω.sub.o) Sin (ω.sub.i - ω.sub.o)t (6)

Low pass filter 56, in addition to the above mentioned function, alsoperforms the IF amplifier and filter function as described for low passfilter 52. The output of low pass filter 56 is also connected to aninput of phase compensation circuit 19 which generates at its output asignal having a constant phase difference with respect to the signalpresent at the output of differentiator 18 over a range of frequencies.

The output of phase compensation circuit 16 is connected to both inputsof a multiplier circuit 60 which is, therefore, used as a mathematicalsquarer. The signal present at the output of multiplier circuit 60corresponds to the input signal (2) squared, as follows:

    x.sup.2 Sin.sup.2 (ω.sub.i - ω.sub.o)t         (7)

The output of phase compensation circuit 19 is connected to both inputsof a multiplier 61 which is therefore used as a mathematical squarer.The signal present at the output of multiplier circuit 61 corresponds tothe input signal (5) squared, as follows:

    x.sup.2 Cos.sup.2 (ω.sub.i - ω.sub.o)t         (8)

The output of multiplier circuit 60 is connected to a first input of anadder circuit 62 and the output of multiplier circuit 61 is connected toa second input of adder circuit 62. Adder circuit 62 comprises, forexample, an output and means for generating at that output a signalcorresponding to the mathematical sum of the numbers represented by theinput signal. The output of adder circuit 62 corresponds to

    x.sup.2 = x.sup.2 (Cos.sup.2 (ω.sub.i - ω.sub.o)t + Sin.sup.2 (ω.sub.i - ω.sub.o)t)

A signal translating circuit 70 comprises inputs connected to the outputof adder 62 and optionally to the outputs of differentiators 15 and 18and phase compensation circuits 16 and 19, an output and means forgenerating at that output a signal corresponding to the audio componentof the input signal received by antenna 10. One of three differentcircuits may be used to implement signal translating circuit 70according to the type of modulation of the input signal received byantenna 10 and the transmission characteristics. A first signaltranslating circuit for demodulating the input signal received byantenna 10 by generating an estimate of the power mean frequency of theinput signal is shown in FIG. 2.

An output of differentiator 15 is connected to one input of a multiplier71, and the output of phase compensation circuit 19 is connected toanother input of multipler 71 which generates at its output a signalcorresponding to the product of the two input signals, as follows:

    x.sup.2 (ω.sub.i - ω.sub.o) Cos.sup.2 (ω.sub.i - ω.sub.o)t                                           (9)

The output of differentiator 18 is connected to one input of amultiplier 72 and the output of phase compensation circuit 16 isconnected to the other input of multiplier 72 which generates an outputsignal corresponding to the product of the input signals, as follows:

    -x.sup.2 (ω.sub.i - ω.sub.o) Sin.sup.2 (ω.sub.i - ω.sub.o)t                                           (10)

The output of multiplier 71 is connected to the minuend input ofsubtractor circuit 73, and the output of multiplier 72 is connected tothe subtrahend input of subtractor 73. The output of subtractor 73represents a number which corresponds to the difference between thenumbers represented by the signals present on the minuend input and thesubtrahend input, as follows:

    x.sup.2 (ω.sub.i - ω.sub.o)                    (11)

The output of subtractor circuit 73 is connected to the input of anintegrator circuit 74 which generates at its output a signalcorresponding to the time average of its input signal over a predefinedperiod of time. The output of adder 62 is connected to the input of anintegrator 75. The output of integrator 74 is connected to the dividendinput of a divider circuit 76, and the output of integrator circuit 75is connected to the divisor input of divider circuit 76. The output ofdivider circuit 76 represents a number corresponding to the numberrepresented by the signal present on the dividend input divided by thenumber represented by the signal present on the divisor input. Theoutput of divider circuit 76 represents the power mean frequency of theinput signal received by antenna 10 which corresponds to the audiocomponent of the frequency modulated input signal. The output of dividercircuit 76 is connected to the input of a de-emphasis circuit 46. Theoutput of de-emphasis circuit 46, which is also the output of signaltranslating circuit 70, is connected to the input of an audio amplifier43 which generates at its output a signal of sufficient amplitude todrive an acoustic signal generating means 44.

A signal translating circuit is shown in FIG. 3 for generating a signalcorresponding to the instantaneous frequency of the input signal presentat antenna 10. The instantaneous frequency also corresponds to the audiocomponent of a frequency modulated signal. The instantaneous frequencyand the power mean frequency each have advantages under certain inputsignal conditions. Multipliers 71 and 72 and subtractor 73 are connectedin FIG. 3 in the same manner as in FIG. 2. The output of subtractor 73is connected to the dividend input of divider circuit 81, and the outputof adder circuit 62 is connected to the divisor input of divider circuit81. The output of divider circuit 81, which corresponds to theinstantaneous frequency of the input signal present at antenna 10, isconnected to the input of an integrator circuit 82 which generates atits output a signal corresponding to the time average of the signalpresent on its input. The output of integrator circuit 82 is connectedto the input of a de-emphasis circuit 83. The output of de-emphasiscircuit 83 is also the output of signal translating circuit 70 and is,therefore, connected to the input of audio amplifier 43.

A signal translating circuit for generating a signal corresponding tothe amplitude of the signal present at antenna 10 is shown in FIG. 4.The output of adder circuit 62 is connected to the input of a squareroot circuit 45 which generates at its output a signal representing themathematical square root of the number represented by its input signal.The output of square root circuit 45 corresonds to the instantaneousamplitude of the input signal present at antenna 10. The output ofsquare root circuit 45 is connected to integrator circuit 91 whichgenerates at its output a signal corresponding to the time average ofits input signal over a predefined period of time. The output ofintegrator circuit 91 is also the output of the signal translatingcircuit 70 and represents the audio component of an AM signal present atantenna 10. The output of integrator circuit 91 is, therefore, connectedto the input of audio amplifier 43. An alternate signal translatingcircuit for generating a signal corresponding to the amplitude of thesignal present at antenna 10 comprises the series connection of anintegrator circuit, a square root circuit, and a low pass filtercircuit. The output of the low pass filter circuit would be connected toaudio amplifier 43.

One exemplary implementation of an FM detector utilizing a signaltranslating circuit which provides at its output a signal correspondingto the power mean frequency of the received FM signal is shown in FIG.7. The implementation shown in FIG. 7 utilizes well known elements, forexample, resistors, capacitors, operational amplifiers, mixers, andmultipliers. Each functional block in FIG. 7 corresponds to a functionalblock shown in FIG. 2 and the implementation of each of these blocksusing the above-mentioned elements is also well known in the art and isincluded here merely as an exemplary implementation.

A splitter circuit 50 comprises three resistors, 101, 102, and 103,connected in a Y arrangement in order to split the input signal into twobranches, each of which corresponds to the input signal. Mixers 51 and55 are commercially available blocks which perform the function ofmixing two input signals to provide an output signal having frequencycomponents equal to both the sum and the difference of the inputfrequency components. Low pass filter 56 comprises an input resistor 104connected from the filter input to the negative input of operationalamplifier (op amp) 105, a ground connection to the positive input of opamp 105, and RC network comprising in parallel resistor 106 andcapacitor 107 is connected in a feedback path between the output of opamp 105 and its negative input. The output of op amp 105 comprises thelow pass filter output. The circuit shown as low pass filter 56 is aso-called active filter whose characteristics are determined by thevalues of resistors 104 and 106 and capacitor 107. Low pass filter 52comprises a similar circuit.

Phase compensator 19 which is basically a low pass filter comprises asecond order active filter which is the equivalent of two first orderactive filters such as used to implement low pass filter 56 in series.The phase compensator 19 comprises resistors 108, 109, 110, 111, and112, capacitors 113 and 114 and op amp 115 connected as shown in FIG. 2.Phase compensator 16 comprises a similar circuit.

Differentiator circuit 18 comprises a resistor 117 and a capacitor 118connected in series between the differentiator input and the negativeinput of op amp 119. The positive input of op amp 119 is connected toground and a parallel RC network comprising a resistor 120 and acapacitor 121 is connected in the feedback path between the output of opamp 119 and its negative input. The output of op amp 119 comprises theoutput of differentiator 18. The characteristics of differentiatorcircuit 18 are determined by the values of the resistors and capacitorsas shown. Differentiator circuit 15 comprises a similar circuit. Anideal differentiator circuit would not require resistor 117 andcapacitor 121. However, it is desirable to reduce the gain of op amp 119above the highest frequency of interest rather than allowing it tocontinuously increase in an ideal fashion. Resistor 117 and capacitor121 perform this function of gain reduction above the highest frequencyof interest.

A multiplier circuit 60 comprises a commercially available multiplier123 having its inputs connected to the inputs of multiplier circuit 60and an op amp 124 which provides an appropriate gain in signal strength.The outputs of multiplier circuit 123 are connected to the correspondinginputs of op amp 124 by resistors 125 and 126. A resistor 127 isconnected from the positive input of op amp 124 to ground and a resistor128 is connected in the feedback path between the output of op amp 124and its negative input. The output of op amp 124 comprises the output ofmultiplier 60. Multiplier circuit 61 comprises a similar circuit andboth multiplier circuits 60 and 61 are utilized to perform amathematical squarer function by connecting both inputs to an inputsignal representing a number to be squared. Multiplier circuits 71 and72 comprise similar circuits used to perform mathematicalmultiplication.

An adder circuit 62 comprises resistors 130 and 131 connected betweenrespective inputs of adder circuit 62 and the negative input of an opamp 132. Op amp 132 has its positive input connected to ground and aresistor 133 connected in a feedback path between the output and thenegative input of op amp 132. The output of op amp 132 comprises theoutput of adder circuit 162.

A subtractor circuit 73 comprises a resistor 135 connected between thesubtrahend input of subtractor circuit 73 and the negative input of anop amp 136, a resistor 137 connected between the minuend input ofsubtractor circuit 73 and the positive input of op amp 136, a resistor138 connected between the positive input of op amp 136 and ground, and aresistor 139 connected in a feedback path between the output of op amp136 and its negative input. The output of op amp 136 comprises theoutput of subtractor circuit 73.

An integrator circuit 75 comprises a resistor 141 connected between theinput of integrator 75 and the negative input of an op amp 142, and RCnetwork comprising resistor 143 and capacitor 144 in parallel isconnected in a feedback path between the output of op amp 142 and itsnegative input and a connection between the positive input of op amp 142and ground. The output of op amp 142 comprises the output of integratorcircuit 75. Integrator circuit 74 comprises a similar circuit. It shouldbe noted that integrator circuit 75 and low pass filter circuit 56 areidentical in terms of the components and their interconnection; however,the values of those components will be determined according to differentrequirements in order to perform the indicated function. An idealintegrator circuit which would perform an integration or averagingfunction over all time up to the present would not require a resistor143. However, the integrators 74 and 75 are designed to be lossyintegrators, i.e., their output represents integration only over apredetermined prior time interval and the effect of inputs before thatpredetermined time interval will be dissipated by resistor 143.

The divider circuit 76 comprises a multiplier circuit 146 with one inputconnected to the divisor input of divider circuit 76 and the other inputconnected to the output of op amp 147 in a feedback path. The output ofmultiplier 146 is connected through a resistor 148 to the negative inputof op amp 147. The divident input of divider circuit 76 is alsoconnected to the negative input of op amp 147 through a resistor 149.The positive input of op amp 147 is connected to ground and its outputcomprises the output of divider circuit 76.

What has been described is considered to be only a specific illustrativeembodiment of the invention and it is to be understood that variousother arrangements may be devised by one skilled in the art withoutdeparting from the spirit and scope thereof as defined by theaccompanying claims.

What is claimed is:
 1. A receiver for producing signals corresponding tothe modulating signals of applied frequency modulated and amplitudemodulated radio frequency signals comprising:an antenna; radio frequencyamplification means comprising: an input connected to said antenna; anoutput terminal; and means for generating a signal at said outputterminal corresponding to a signal present at said input amplified by apredefined factor; and a demodulation circuit comprising:an input; anoutput; switch means comprising:a first input; a second input; a thirdinput; an output connected to said demodulation circuit output; andmeans for selectively connecting one of said first, second, and thirdinputs of said switch means to said switch means output; anddemodulation means for generating: at said switch means first input asignal corresponding to the instantaneous amplitude of an input signalapplied to said receiver antenna utilizing: a first circuit forgenerating a first signal corresponding to the instantaneous power ofsaid applied signal, a circuit for generating a signal corresponding tothe square root of said first signal, and a first integrator circuit forintegrating said square root signal, said integrated square root signalbeing applied to said switch means first input; at said switch meanssecond input a signal corresponding to the instantaneous frequency of aninput signal applied to said receiver antenna utilizing: said firstcircuit and a second circuit for generating signals correspondingrespectively to the instantaneous power and instantaneous powerfrequency product of said applied signal, a divider circuit forproviding a signal corresponding to the ratio of said instantaneouspower frequency product signal to said instantaneous power signal, and asecond integrator circuit for integrating said ratio signal, saidintegrated ratio signal being applied to said switch means second input;and at said switch means third input a signall corresponding to anestimate of the power mean frequency of said applied signal utilizing:said first and second circuits for generating said instantaneous powerand said instantaneous power frequency product signals, said first andsecond integrator circuits for integrating said instantaneous power andsaid instantaneous power frequency product signals and a divider circuitfor providing said estimate of said power mean frequency signalcorresponding to the ratio of said integrated power frequency productsignal to said integrated instantaneous power signal, said estimate ofsaid power means frequency signal being applied to said switch meansthird input.
 2. A receiver for producing signals corresponding to themodulating signals of applied frequency modulated radio frequencysignals comprising:an antenna; radio frequency amplification meanscomprising:an input connected to said antenna; an output terminal; andmeans for generating a signal at said last mentioned output terminalcorresponding to a signaal present at said input amplified by apredefined factor; and a demodulation circuit comprising:an input; anoutput; and means for generating at said demodulation circuit output asignal corresponding to an estimate of the power mean frequency of saidapplied signal utilizing: a circuit for generating a signalcorresponding to the instantaneous power of said applied signal and acircuit for generating a signal corresponding to the instantaneous powerfrequency product of said applied signal, first and second integratorcircuits for integrating said instantaneous power and said instantaneouspower frequency product signals and a diviider circuit for providingsaid estimate of said power mean frequency signal corresponding to theratio of said integrated power frequency product signal to saidintegrated instantaneous power signal.
 3. A receiver for producingsignals corresponding to the modulating signals of applied frequencymodulated radio frequency signals comprising:an antenna; radio frequencyamplification means comprising:an input connected to said antenna; anoutput terminal; and means for generating a signal at said lastmentioned output terminal corresponding to a signal present at saidinput amplified by a predefined factor; and a demodulation circuitcomprising:an input; an output; and means for generating at saiddemodulation circuit output a signal corresponding to the instantaneousfrequency of an input signal applied to said receiver antenna utilizing:first and second circuits for generating signals correspondingrespectively to the instantaneous power and instantaneous powerfrequency product of said applied signal, a divider circuit forproviding a signal corresponding to the ratio of said instantaneouspower frequency product signal to said instantaneous power signal, andan integrator circuit for integrating said ratio signal.
 4. A receiverfor producing signals corresponding to the modulating signals of appliedamplitude modulated radio frequency signals comprising:an antenna; radiofrequency amplification means comprising:an input connected to saidantenna; an output terminal; and means for generating a signal at saidlast mentioned output terminal corresponding to a signal present at saidinput amplified by a predefined factor; and a demodulation circuitcomprising:an input; an output; and means for generating at saiddemodulation circuit output a signal corresponding to the instantaneouspower of an input signal applied to said receiver antenna utilizing: acircuit for generating a first signal corresponding to the instantaneouspower of said applied signal, a circuit for generating a signalcorresponding to the square root of said first signal, and an integratorcircuit for integrating said square root signal.
 5. A spectral parameterestimator for use as a demodulator comprising:a spectral parameterestimator input terminal for receiving an input signal; a spectralparameter estimator output terminal; a reference signal generatorcomprising:a first output; a second output; and means for generatingsignals at said first and second outputs corresponding to the Sine andCosine, respectively, of a reference signal frequency times a timefactor; a first mixer comprising:a first input connected to said inputterminal; a second input connected to said first output of saidreference signal generator; an output; and means for generating anoutput signal corresponding to the Sine of the difference between saidinput signal frequency and said reference signal frequency plus the Sineof the sum of said input signal frequency and said reference signalfrequency; a first low pass filter comprising:an input connected to saidoutput of said first mixer; an output; aand means for generating on saidoutput a signal corresponding to the Sine of said input signal frequencyminus said reference signal frequency; a second mixer comprising:a firstinput connected to said input terminal; a second input connected to saidsecond output of said reference signal generator; an output; and meansfor generating an output signal corresponding to the Cosine of thedifference between said input signal frequency and said reference signalfrequency plus the Cosine of the sum of said input signal frequency andsaid reference signal frequency; a second low pass filter comprising: aninput connected to said output of said second mixer;an output; and meansfor generating on said output a signal corresponding to the Cosine ofsaid input signal frequency minus said reference signal frequency; afirst differentiator circuit comprising:an input connected to saidoutput of said first low pass filter circuit; an output; and means forgenerating an output signal corresponding to the derivative of thesignal applied to said input of said first differentiator circuit; asecond differentiator circuit comprising:an input connected to saidoutput of said second low pass filter circuit; an output; and means forgenerating an output signal corresponding to the derivative of thesignal applied to said input of said second differentiator circuit; apower circuit comprising:first and second inputs connected respectivelyto said first low pass filter circuit and said second low pass filtercircuit; an output; and means for generating an output signalcorresponding to the power of an input signal applied to said spectralparameter estimator input terminal; a signal translating circuitcomprising:inputs connected to said outputs of said first and second lowpass filter circuits, said first and second differentiator circuits, andsaid power circuit; an output connected to said spectral parameterestimator output terminal; and means for generating a signal at saidoutput corresponding to the demodulated audio component of an inputsignal applied to said spectral parameter estimator input as representedby said inputs to said signl translating circuit.
 6. A spectralparameter estimator according to claim 5 wherein said signal translatingcircuit further comprises:a power frequency product circuitcomprising:inputs connected to said outputs of said first and second lowpass filter circuits and said first and second differentiator circuits;an output; and means for generating an output signal corresponding tothe product of the power of said input signal and the difference betweensaid input signal frequency and said reference signal frequency; a firstintegrator comprising:an input connected to said output of said powerfrequency product circuit; an output; aand means for generating anoutput signal corresponding to the average power frequency product ofsaid input signal and said reference signal over a predetermined periodof time; a second integrator circuit comprising:an input connected tosaid output of said power circuit; an output; and means for generatingan output signal corresponding to the average power of said inputsignal; a divider circuit comprising:a dividend input connected to saidoutput of said first integrator; a divisor input connected to saidoutput of said second integrator; an output connected to said outputterminal; and means for generating an output signal corresponding to thepower mean frequency of said input signal.
 7. A spectral parameterestimator according to claim 5 wherein said signal translating circuitfurther comprises:a power frequency product circuit comprising:inputsconnected to said outputs of said first and second low pass filtercircuits and said first and second differentiator circuits; an output;and means for generating an output signal corresponding to the productof the power of said input signal and the difference between said inputsignal frequency and said reference signal frequency; a divider circuitcomprising: a dividend input connected to said output of said powerfrequency product circuit; a divisor input connected to said output ofsaid power circuit; an output; and means for generating an output signalcorresponding to the instantaneous frequency of said input signal; anintegrator circuit comprising: an input connected to said output of saiddivider circuit; an output connected to said output terminal; and meansfor generating an output signal corresponding to the averageinstantaneous frequency over a predetermined period of time.
 8. Aspectral parameter estimator according to claim 5 wherein said signaltranslating circuit further comprises:a square root circuitcomprising:an input connected to said output of said power circuit; anoutput; and means for generating an output signal corresponding to themathematical square root of the nmber represented by said input signal;an integrator circuit comprising:an input connected to said output ofsaid square root circuit; an output connected to said output terminal;and means for generating an output signal corresponding to the averageamplitude of said input signal over a predetermined period of time.
 9. Aspectral parameter estimator according to claim 5 further comprising:asplitter circuit connected between said input terminal and said firstmixer circuit and said second mixer circuit comprising:an inputconnected to said input terminal; a first output; a second output; andmeans for generating at said first and said second outputs signalscorresponding to signals present on said splitter circuit input.
 10. Aspectral parameter estimator according to claim 6 further comprising:afirst phase compensation circuit connected between said first low passfilter output and said power circuit comprising:an input connected tosaid output of said first low pass filter; an output connected to aninput of said power circuit; and means for generating a signal at saidfirst phase compensation circuit output corresponding to the signalpresent at said first phase compensation circuit input phase shiftedwhereby said output of said first differentiator and said output of saidfirst phase compensation circuit have a substantially constant phaserelationship over a certain range of frequencies; and a second phasecompensation circuit connected between said second low pass filteroutput and said power circuit comprising:an input connected to saidoutput of said second low pass filter; an output connected to an inputof said power circuit; and means for generating a signal at said secondphase compensation circuit output corresponding to the signal present atsaid second phase compensation circuit input phase shifted whereby saidoutput of said second differentiator and said output of said secondphase compensation circuit input phase shifted whereby said output ofsaid second differentiator and said output of said second phasecompensation circuit have a substantially constant phase relationshipover a certain range of frequencies.
 11. A spectral parameter estimatoraccording to claim 5 wherein said signal translating circuit furthercomprises:an integrator circuit comprising:an input connected to saidoutput of said power circuit; an output; and means for generating anoutput signal corresponding to the time average of a signal present atsaid integrator input; a square root circuit comprising:an inputconnected to said output of said integrator circuit; an output; andmeans for generating an output signal corresponding to the mathematicalsquare root of the number represented by the signal present at saidsquare root circuit input; a low pass filter circuit comprising:an inputconnected to said output of said square root circuit; an outputconnected to said output terminal; and means for generating an outputsignal corresponding to certain low frequency components of the signalpresent on said low pass filter input.